3,4-Methylenedioxymethamphetamine (MDMA) abuse is a serious health problem yet little is known about its effects on developing brain. We established that neonatal rats administered MDMA (a model of 3rd trimester exposure) causes long-term path integration and spatial learning and memory impairments after P11-20 (but not P1-10) exposure, while sparing cued and working memory. New data show that exposed offspring have altered expression of CAPON, PSD95, nNOS, and NMDA-NR1 (all members of the NMDA receptor complex). This treatment also causes large reductions in 5-HT and sustained release of corticosterone (CORT). P11-20 overlaps the stress hyporesponseive period (SHRP, P4-15). We hypothesize that MDMA treatment that begins during the SHRP triggers a unique cascade of events beginning with overactivation of the stress response pathway (release of CRF, ACTH, CORT) but in which normal feedback mechanisms fail to operate correctly. The resulting prolonged CORT release alone or combined with the concomitant 5-HT reductions lead to changes in CNS organization and long-term cognitive deficits. Specific aims to test this hypothesis are: (1a) Determine the critical period for MDMA-induced long-term cognitive and NMDA receptor complex effects using treatment intervals before, during and after the SHRP and for changes in response to stress. (1b) Compare the critical period from Aim 1a with a non-critical period for short-term effects on the HPA axis and brain 5-HT. (2) Test the role of HPA axis changes in the long-term effects using a new technique we developed involving adrenalectomy combined with adrenal alloengraftment to temporarily interrupt HPA responses with later restoration of basal CORT function. (3) Test 5-HT involvement by blocking MDMA-induced 5-HT reduction using SSRI pretreatment and test for prevention of cognitive deficits. (4) Determine changes .in nNOS, NMDA-NR1, PSD-95 and CAPON and related proteins in animals not tested behaviorally to ensure that these changes are not experience-dependent. The present model of developmental MDMA exposure is the first to establish induction of cognitve deficits and is the first step in our long range objective to ultimately test the effects of MDMA after exposure during other (earlier) stages of brain development.